Laminated muntin bar method

ABSTRACT

An exemplary embodiment of the invention concerns a process for forming an elongated strip for use in making two tone muntin bars. An elongated strip of muntin bar material is provided that has been treated on at least a portion of one side to define an exposed surface of a completed muntin bar fabricated from the muntin bar material. An elongated strip of covering material is also provided for controlled application onto a specified portion of a surface of the muntin bar material. The elongated strip of covering material includes an adhesive for adhering the covering material to the muntin bar material. The muntin bar material and the covering material are brought into contact with each other thereby causing the covering material to overlie and adhere to the muntin bar material.

This application is a Divisional of Ser. No. 09/781,630, filed Feb. 12,2001, and now U.S. Pat. No. 6,687,982.

FIELD OF THE INVENTION

The present invention concerns muntin bars used for separating windowpanes of large size into smaller size panes to enhance the appearance ofa window.

BACKGROUND ART

Windows constructed from multiple glass panes utilized “muntins” or“muntin bars” to secure the edges of the individual glass panes withinthe window sash. In many windows, muntins formed distinctive gridpatterns that are associated with architectural styles of buildingscontaining the windows.

Modern windows formed by insulating glass units utilize single glasslights separated by an insulating dead air space. Where a particulararchitectural “look” is desired, a grid of muntin bars is fixed in thedead air space between the glass lights to simulate a multi-pane window.Typical muntin bars for insulating glass units are formed fromdecoratively coated interfitted metal tubes. The grids are anchored tothe insulating glass unit periphery.

Constructing muntin bar grids for insulating glass units has been alabor intensive process. As a consequence, manufacturing such units, andthus windows formed by the units, has been costly and inefficient. Someefforts to mechanize the manufacture of muntin grids have been made.Commonly owned U.S. Pat. No. 6,173,484 entitled “System for FabricatingMuntin Bars from Sheet Material” which issued Jan. 16, 2001 to McGlinchyet al. is an example of a system for automated fabrication of muntinbars. The subject matter of this patent is incorporated herein byreference. Commonly owned pending U.S. patent application Ser. No.09/525,349 entitled “System for Fabricating Contour Muntin Bars fromSheet Material” is a second patent application to McGlinchy et alconcerning automated fabrication of so-called contour muntin bars andthe subject matter of this application is incorporated herein byreference.

The muntin bar stock is produced by roll forming decoratively coatedsheet material such as aluminum or steel, in a known manner. Varioussizes of the sheet material are used to form different size muntin barstock. The roll forming machine has a series of rolls configured to formsheet material into elongated tubular muntin bar stock. A windowmanufacturer purchases the muntin bar stock size(s) needed to produceinsulating glass units. Apparatus disclosed in the aforementioned patentapplication also cuts the stock into lengths that are notched inappropriate locations for assembly into grids for incorporation into theinsulating glass units.

The residential window and door industry has witnessed an increaseddemand for internal decorative muntin bars contained in insulated glass(IG) units of their windows. This market demand for muntin bars hasincreased due to popular “colonial look” trends in the market which hasincreased the demand for simulated wood grain finishes for muntin bars.Also contributing to the demand are new construction and residentialbuilding codes requiring a common facade in local neighborhoods. Withpeople also desiring differentiation and designer choices in theirwindows, a demand for so-called “two tone” muntin bars is on the rise.The two tone muntin bar present one appearance from the outside and asecond appearance from inside the window.

Two-tone muntin bars are offered today in many color combinations forboth rectangular and contour style muntin bars. A two-tone muntin bardemands a premium price in the market place. One reason for theincreased price of two tone muntin bars is the fact that automatedmanufacturing of two tone muntin bars using controlled notching, rollforming and severing has not occurred.

The most common method practiced at the present time for manufacturingtwo tone muntin grids starts with a long roll formed bar that is oftenshipped to a secondary supplier that paints or laminates the bar with asolid color tone or pattern on one side and a second color or pattern onthe opposite side. Use of multiple steps performed by multiple suppliersresults in significant additional cost to the product. More elaboratebars have simulated wood grains that are used to match up with the woodtrim in or surrounding the window sash. All of the current methodsrequire cutting specified length segments from a two tone bar. This baris then mitred and/or punched to complete fabrication of the muntin bar.The current methods require post painting and/or lamination which aretime consuming, costly and provide limited throughput. This requirementalso leads to a build up of inventory to give the suppliers adequatelead time for performing these post roll forming procedures.

SUMMARY OF THE INVENTION

The present invention concerns an automated method and apparatus forproducing laminated muntin tailstock material before muntin bars areroll formed into either rectangular or contour muntin bars. Inaccordance with one process two tone muntin bars are provided that haveone appearance when viewed from outside the window and a secondappearance when viewed from inside the window.

An exemplary embodiment of the invention concerns a process for formingan elongated strip for use in making muntin bars. An elongated strip ofmuntin bar material is provided that has been treated on at least aportion of one side to define an exposed surface of a completed muntinbar fabricated from the muntin bar material. An elongated strip ofcovering material is also provided for controlled application onto aspecified portion of a surface of the muntin bar material. The elongatedstrip of covering material includes an adhesive for adhering thecovering material to the muntin bar material. The muntin bar materialand the covering material are brought into contact with each otherthereby causing the covering material to overlie and adhere to themuntin bar material.

One aspect of the invention is used in making muntin bars that arecompletely covered. An example of such a muntin bar includes a pattern,such as a simulated grain pattern, on both the inside and the outside ofthe window. The invention can also be used to make two tone muntin barsthat present different appearances on the inside and outside of thewindow.

When making two tone muntin bars, one exemplary embodiment of theinvention starts with an elongated strip of muntin bar material that hasbeen painted on at least one side. A covering material is brought intocontact with a painated surface of the muntin bar material. For the twotone application, the covering material covers one half of an exterior,painted surface of the muntin bar material to form a composite strip.When bent into a muntin bar one side of the muntin bar has a firstappearance and a second side of the muntin bar has a second appearance.

Practice of the invention allows the laminated muntin bars to beproduced on an as needed basis. A coil of strip that has been paintedwith an appropriate color is stored in inventory rather than acollection of fabricated muntin bars which must be shipped to a supplierand then shipped back to the window fabricator for inclusion in an IGU.

The disclosed embodiment of the invention uses a flexible elongatedmultilayer strip or foil of covering material that is applied to thepainted surface of the muntin bar material. A first layer has anappearance which is visible on a muntin bar fabricated from themutlilayer strip. A second adhesive layer causes the first, appearancedefining layer to adhere to a strip of muntin bar material. The foilalso includes a carrier layer for supporting the first layer as themultilayer strip or foil is brought into contact with a muntin barstrip.

These and other objects, advantages and features of the invention willbecome better understood from a review of the exemplary embodiment ofthe invention which is described in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an insulating glass unit including amuntin bar grid;

FIG. 2 is an enlarged perspective view of a portion of the muntin bargrid of the insulating glass unit of FIG. 1;

FIG. 3 is a plan view of a portion of stock material partially processedaccording to the invention;

FIG. 4 is an elevation view schematically illustrating forming the stockmaterial of FIG. 3 into a muntin bar;

FIG. 5 is a schematic depiction of a process for forming an elongatedcoiled strip of material from which a two tone muntin bar can befabricated;

FIG. 6 is a schematic depiction showing a starting strip of materialwhich is adhered to form a strip for manufacturing two tone muntin bars;

FIG. 7 is a perspective view of a contour muntin bar that includes alamination for achieving a wood grain appearance on both sides of themuntin bar;

FIG. 8 is an enlarged perspective view of a portion of an insulatingglass unit having a laminated muntin bar fabricated in accordance withthe present invention; and

FIG. 9 is a top plan view of a region of a heat controlled pressureroller that forms a nip region.

BEST MODE FOR PRACTICING THE INVENTION

FIG. 1 shows an insulating glass unit indicated generally by thereference numeral 10 comprising a spacer assembly 12 sandwiched betweenglass sheets, or lights, 14. The spacer assembly 12 includes a frameassembly 16 hermetically joined to the glass lights by a sealant 18 toform a closed dead air space 20 between the lights. The unit 10 isillustrated in FIG. 1 is in condition for assembly into a window or doorframe (not shown).

A muntin bar grid indicated at G is disposed between the glass lights toprovide the unit 10 with the appearance of a multi-pane window. As seenin FIG. 2, the illustrated grid G is comprised of muntin bars M havingmating notches 22 interfitted at an intersection I. In certain instancesthe bars M are secured together by a suitable adhesive indicated at A,but a more common technique secures together two muntin bars with aflexible cross shaped clip that extends a short distance into each ofthe two intersecting muntin bars M. The ends of the muntin bars M aresecured to the interior of the spacer frame 16 by suitable fasteners asis known in the art.

FIG. 3 shows a length of a strip S of stock material that is to beformed into a muntin bar M according to the invention. An outer surface24 of the strip S is painted to have a desired color. This first coloris the color presented to an observer from one side of the completedinsulating glass unit 10. The strip S is made from a thin elongatedmetal, for example, aluminum or steel that can be wound into anelongated strip as disclosed in the pending patent application toMcGlinchy et al. noted above. The two tone appearance of the muntin barM is achieved by applying a coating or covering layer 150 (FIG. 6) toone side of the strip. The process for applying this coating isdescribed in greater detail below.

According to the fabrication process disclosed in the McGlinchy et al.patent application, the strip S is fed lengthwise through a muntin barproduction line including a series of forming stations and is formedinto a muntin bar M having a notch 22 for interfitting with the notch ofanother muntin bar. The strip S (FIG. 3) includes opposite edges 30 a,30 b that, along with fold lines 32 a, 32 b, define a pair of end panels34 a, 34 b. The fold lines 32 a, 32 b, along with fold lines 32 c, 32 d,define a pair of intermediate panels 36 a, 36 b. The fold lines 32 c, 32d define a central panel 38. The notch 22, shown in phantom, extendsinward from edge 30 a of the stock material illustrated in FIG. 3 to thecenterline 28. In an embodiment described in more detail below, one halfof the stock material S is covered to produce a different muntin barappearance on opposite sides of the completed IG unit. For thisembodiment, the notch 22 must, for some of the interfitting bars, extendinward toward the stock centerline from the edge 30 b rather than theside 30 a shown in FIG. 3 so that the completed muntin bar grid has anappropriate appearance.

FIG. 4 schematically indicates a progressive change in the shape of thestrip S from a flat strip to a rectangular cross section structure asthe strip passes through a multiple stage roll forming apparatus (notshown). The strip S is bent in the region of the fold lines 32 a, 32 b,32 c, 32 d to form an enclosed structure having rectangular borders asseen from the end. When severed from the end of the strip S thisstructure forms a muntin bar M that is interfitted with one or moreother bars to form a grid G such as the grid of FIG. 1.

As can be seen in FIG. 4, the muntin bar M includes an outer surface 24.The outer surface 24 includes a first outwardly facing half portion 24 athat would be visible to a person looking through the IG unit 10 fromone side of the unit 10 and a second outwardly facing half portion 24 bthat would be visible to a person looking through the IG unit 10 fromthe opposite side of the unit. In one embodiment of the presentinvention, an outer surface 24 of the strip S is painted or otherwisetreated to have a first appearance and a portion of the outer surface24, approximately half its width, is covered with the coating layer 150having a second appearance.

Bending of the strip S as depicted in FIG. 4 produces a two tone muntinbar M, that is, a muntin bar that has the first appearance on theoutwardly facing surface 24 a and the second appearance on the outwardlyfacing surface 24 b. The enlarged perspective view shown in FIG. 8 showssuch an insulating glass unit 10. Alternatively, the outer surface 24 ofthe strip S is completely covered with the coating layer 150. A contourmuntin bar grid G is depicted in FIG. 7 having coating over the entiresurface so that subsequent to a roll forming process described in theMcGlinchy et al patent application entitled “System for FabricatingContour Muntin Bars from Sheet Material” the entire outer surface of themuntin bars that make up the grid G is covered with a wood grainsimulated finish.

FIG. 5 discloses a system 110 for fabricating an elongated strip S foruse in making two tone muntin bars M such as the bars depicted in FIG.2. A first rotatably mounted supply 114 unwinds a first elongated strip116 of flexible muntin bar material that is a first constituentcomponent of the strip S. The strip 116 has been treated on at least oneside to define an exposed surface 24 of a completed muntin bar that isfabricated from the strip S. In the exemplary embodiment of theinvention, the strip 116 is treated by painting.

In an exemplary embodiment of the invention, the paint applied to thesurface 24 is a thermoplastic polyester base formulated to inhibit theoffgassing of any volatile contaminants created in the process offabricating IG units and thus will not fog when processed through highenergy infrared ovens used to fabricate IG units. Suitable paints may beobtained under the tradename “Specialty Super Series 1000” fromSpecialty Coating Company, Inc. of Elk Grove Village, Ill. 60007.Physical properties of this paint are listed below:

Viscosity @ 77 degrees F. 25-30 SEC Viscometer: #4 Zahn Weight/GallonRange 9.0-9.4 LBS Coverage 748 SQ.FT/Gal @ 50 mils Non-Volatile Weight36-38% Non-Volatile Volume 22-24% VOC Range 5.71-5.91 lbs/Gal HMISRating 2-2-0-C

In addition to the first elongated strip 116, the second constituentcomponent of the strip S is a coating or covering material 150 that isapplied onto a desired portion of the painted strip surface, i.e., oneof the outwardly facing surfaces 24 a or 24 b of the painted stripsurface 24. Prior to application to the strip surface 24, the coveringmaterial 150 is part of a second elongated strip or laminating foil 122that is provided from a second rotatably mounted supply 120. Applicationor lamination of the covering material 150 onto a desired portion of thepainted strip surface 24 involves use of heat and the application ofpressure to achieve a transfer of the covering material 150 from thesecond elongated strip 122 onto the painted strip surface 24 as will beexplained below.

Turning to FIG. 6, the second elongated strip 122, sometimes referred toas a hot stamp lamination foil, comprises a carrier layer 210, typicallya polyester film, which provides a backing or substrate for the strip122. A release layer 212 is adhered to the carrier layer 210 and, inturn, the covering material 150 is adhered to the release layer 212. Therelease layer 212 preferably is a lacquered resin with a low meltingpoint. During the lamination or application process, when the strip 122is sufficiently heated the release layer 212 melts thereby releasing orseparating the covering material 150 from the carrier layer 210.Pressure applied causes the covering material 150 to be adhesivelyaffixed to the painted strip surface 24.

In one exemplary embodiment, the covering material 150 is comprised ofthree layers: a decorative color or printed layer 216, a protectivelayer 214 and an adhesive layer 218. The protective layer 214 isoptional, but depending on its composition, can protect the decorativecolor layer 216 from scratching, chemical attack and UV (ultra violet)fading.

The decorative color layer 216 may be a desired paint color or a printedimage, e.g., a wood grain finish appearance. The decorative color layer216 is typically an ink lacquer which dries very rapidly by release ofsolvent. After application of the covering material 150 to the paintedstrip surface 24, the protective layer 214 functions as an outerprotective surface for the decorative color layer 216 to protect thecolor layer 216 from scratching, resists chemicals and reflects UVradiation.

The third component of the covering material 150 of the strip 122 is theadhesive layer 218. The adhesive layer 218 comprises an adhesive that isformulated for compatibility with the paint applied to the strip surface24 as well as the decorative color layer 214. The adhesive layer 218 istypically comprised of a combination of resins (lacquers) that cure fromapplied heat and chemically cross link the decorative color layer 216 tothe paint applied to the strip surface 24. Additionally, the adhesivelayer 218 adheres to the strip surface 24 and is sufficiently elastic sothat the elongated strip of stock material S can be rollformed withoutdelamination of the covering material 150 or scratching either thecovering material 150 or in the case of a two tone muntin bar scratchingthe painted outer surface of the bar. This roll forming results ineither a rectangular cross section shaped muntin bars M as describedabove and shown schematically in FIG. 4 or in a contour muntin bar forforming a muntin bar grid G as depicted in FIG. 7.

Returning to FIG. 5, the system 110 for fabricating the elongated stripS from the first strip 116 of aluminum or steel and the coveringmaterial 150 released from the lamination foil 122 includes a drivesystem (discussed below) for simultaneously unwinding the muntin barmaterial 116 and the covering material 150 and bringing them intocontact with each other to cause the covering material 150 to overlieand adhere to a portion of the surface 24 of the muntin bar material116. In the disclosed exemplary embodiment of the invention the coveringmaterial 150 covers one half of the outwardly facing surface 24 of thestrip 116, namely one of the surface portions 24 a or 24 b. A pressureroll 123 defines a nip 124 for applying pressure to a region ofengagement between the muntin bar material strip 116 and the laminationfoil 122.

Once the covering material 150 has been applied to a portion of thestrip 116 resulting in the finished muntin bar strip S, the strip S isrewound onto a recoiler 130 downstream from the nip 124. From therecoiler 130 the coil strip of material is transported to a system suchas that shown in the McGlinchy et al patent application for bending intothe muntin bars. Alternatively, the processing station could be coupleddirectly to such a system for immediate processing of the strip S intomuntin bars.

The covering material 150 of the lamination foil 122 is transferred ontothe painted aluminum substrate 116 using heat and pressure. During thelamination process, the release layer 212 is melted and the carrierlayer 210 separates from the covering material layer 150 that adhere tothe strip 116. This leaves the layers 214, 216, 218 on one half of theoutside surface of the strip S.

Downstream from the nip 124, the carrier layer 210 is rewound onto arecoiler 151 and the completed strip S is rewound onto the recoiler 130.The recoilers 150, 130 are driven by respective motors 152, 154 havingoutput shafts coupled to their respective recoilers and whose speed ofrotation is coordinated by a programmable controller 160. An opticalencoder 162 positioned next to an idler roller 164 monitors movement ofthe strip S and allows the controller 160 to co-ordinate the speed ofrotation of the two motors 152, 154 to a desired speed setpoint.

Side to side alignment or registration is maintained between the twostrips 116, 122 by guide rollers 166 (FIG. 9) that engage the side ofthe strip 116 after it has been unwound from the supply 114. These guiderollers 166 rotate about generally vertical axes and maintain the stripin side to side alignment near the pressure roll 123. The pressure roll123 is a iron impregnated heat controlled silicon roll. The strip 122 isunwound from its supply 120 and reeved around a guide roller 167 for thelaminating foil 122. The foil 122 and strip 116 are brought together atthe nip between the pressure roll 123 and the steel backing roller 162.On the exit side of the nip 124 the carrier layer passes over a guide168 and rewound on the coil 151. The pressure roll 123 is mounted forside to side movement so that for a strip S such as the one shown inFIG. 9, the pressure roll 123 only contacts the laminating foil 122. Thepressure roll 123 also provides a position adjustment to allowadjustment of the position of the lamination edge.

The pressure roll 123 is biased against a fixed nip defining roll 162mounted for rotation along a path of travel for the strip 116 andlamination foil 122. The pressure roll 123 is a heat controlled ironimpregnated silicone roller. Before reaching the nip 124, the strip 116is directed by a strip guide roller through a controlled preheat chamber172 to preheat the strip 116. Preheating the strip 116 facilities properadhesion of the adhesive layer 218 to the painted surface to producehigh quality lamination at high speeds (greater than 10 feet perminute). The heating cross links bonding between the decorative colorlayer 216 and the painted strip surface 24. Downstream of the nip 124 isa cooling tunnel 174 for cooling the temperature of the fabricatedmuntin bar strip S prior to recoiling the strip S, so the strip does notstick to other layers when rewound.

Experience with the lamination process has identified ranges ofoperating parameters for use in practicing the invention. It has beenfound that the preheat chamber 172 should raise the temperature of thestrip 116 to approximately 200 degrees F. at an exit from the chamber172. Performance has been seen to be adequate when the temperature iswithin a range of 190 degrees to 210 degrees. At the nip 124 thetemperature of the pressure roll 123 has been adquate when maintained atabout 400 degrees F. The cooling tunnel 174 most preferably drops thetemperature of the strip S to a temperature in a range of from 120degrees F.-150 degrees F. Throughputs of between ten and fifty feet perminute have been achieved through practice of the invention and evenhigher throughputs may be achievable.

While the present invention has been described with a degree ofparticularity, it is the intent that the invention include allmodifications and alterations from the disclosed design falling withinthe spirit or scope of the appended claims.

1. A process for making muntin bars comprising the steps of: a) providing an elongated strip of muntin bar material that has been treated on at least a portion of one side to define an outer surface of a completed muntin bar fabricated from the muntin bar material; b) providing an elongated strip of covering material for controlled application onto a specified portion of the treated portion of the muntin bar material, said elongated strip of covering material including an adhesive for adhering the covering material to the muntin bar material; and c) bringing the muntin bar material and the covering material into contact with each other to cause the covering material to overlie and adhere to the muntin bar material and form an elongated strip of stock material which is subsequently bent to form a muntin bar.
 2. The process of claim 1 additionally comprising applying a coating to the elongated muntin bar material by painting the elongated muntin bar material on said one side prior to bringing the covering material into contact with a painted portion of said one side of the muntin bar material.
 3. The process of claim 1 wherein the elongated strip of covering material is a multilayered foil and wherein one layer is an adhesive, a second layer is a plastic film carrier, and a third layer is a release layer and further comprising the step of applying a controlled pressure as the multilayered foil is brought into contact with the muntin bar material to cause the adhesive layer to bond to the muntin bar material.
 4. The process of claim 3 additionally including applying heat to a region of contact between the covering material and the muntin bar material.
 5. The process of claim 4 wherein the muntin bar material is a flexible metal strip of material that is unwound from a coil and then moved through a heating zone prior to bringing the covering material into contact with the said flexible metal strip.
 6. The process of claim 5 wherein a combined strip of flexible metal strip and adhering covering material is moved through a cooling region downstream from a region wherein the covering material is applied to the metal strip.
 7. The process of claim 6 wherein a combined strip of flexible metal strip and adhering covering is wound onto a supply downstream from the cooling region.
 8. The process of claim 2 wherein one entire side of the elongated muntin bar material is painted to provide a painted surface and wherein one half of said painted surface is covered with the elongated strip of covering material to form a two tone muntin bar strip.
 9. The process of claim 4 wherein the applying of heat is performed by a heated contact roll that also applies pressure to a region of engagement between the elongated strip of muntin bar material and the elongated strip of covering material.
 10. The process of claim 1 wherein the elongated strip of stock material is roll formed to form a rectangular muntin bar.
 11. The process of claim 1 wherein the elongated strip of stock material is roll formed to form a contour muntin bar.
 12. The process of claim 1 wherein one complete surface of the stock material is covered with the covering material to define an outer appearance for both sides of a roll formed muntin bar.
 13. A process for making elongated stock material for fabrication into muntin bars comprising the steps of: a) providing an elongated strip of muntin bar material that has been treated on at least a portion of one side to define an outer surface of a completed muntin bar fabricated from the muntin bar material; b) providing an elongated strip of covering material for controlled application onto a specified portion of the treated portion of the muntin bar material, said elongated strip of covering material including an adhesive for adhering the covering material to the muntin bar material; and c) bringing the muntin bar material and the covering material into contact with each other to cause the covering material to overlie and adhere to the muntin bar material and form an elongated strip of stock material which is subsequently bent to form a muntin bar.
 14. The process of claim 13 additionally comprising applying a coating to the elongated muntin bar material by painting the elongated muntin bar material on said one side prior to bringing the covering material into contact with a painted portion of said one side of the muntin bar material.
 15. The process of claim 14 wherein one entire side of the elongated muntin bar material is painted to provide a painted surface and wherein one half of said painted surface is covered with the elongated strip of covering material to form a two tone muntin bar strip.
 16. The process of claim 13 wherein the elongated strip of covering material is a multilayered foil and wherein one layer is an adhesive, a second layer is a plastic film carrier, and a third layer is a release layer and further comprising the step of applying a controlled pressure as the multilayered foil is brought into contact with the muntin bar material to cause the adhesive layer to bond to the muntin bar material.
 17. The process of claim 16 additionally including applying heat to a region of contact between the covering material and the muntin bar material.
 18. The process of claim 17 wherein the muntin bar material is a flexible metal strip of material that is unwound from a coil and then moved through a heating zone prior to bringing the covering material into contact with the said flexible metal strip.
 19. The process of claim 18 wherein a combined strip of flexible metal strip and adhering covering material is moved through a cooling region downstream from a region wherein the covering material is applied to the metal strip.
 20. The process of claim 19 wherein a combined strip of flexible metal strip and adhering covering is wound onto a supply downstream from the cooling region.
 21. The process of claim 17 wherein the applying of heat is performed by a heated contact roll that also applies pressure to a region of engagement between the elongated strip of muntin bar material and the elongated strip of covering material.
 22. A process for making muntin bars, comprising: a) providing an elongated strip of muntin bar material that has been treated on at least a portion of one side to define an outer surface of a completed muntin bar fabricated from the muntin bar material; b) providing an elongated strip of covering material for controlled application onto a specified portion of the treated portion of the muntin bar material, said elongated strip of covering material including an adhesive for adhering the covering material to the muntin bar material; c) bringing the muntin bar material and the covering material into contact with each other to cause the covering material to overlie and adhere to the muntin bar material and form an elongated strip of stock material; d) defining a notch that extends inward from an edge of said stock material; and, e) roll forming the stock material to form a muntin bar having a notch for interfitting with a notch of a second muntin bar.
 23. The method of claim 22 wherein said notch of the second muntin bar is defined by a notch that extends inward from a second edge of said stock material.
 24. A process for making a muntin bar grid, comprising: a) providing an elongated strip of muntin bar material that has been treated on at least a portion of one side to define an outer surface of a completed muntin bar fabricated from the muntin bar material; b) providing an elongated strip of covering material for controlled application onto a specified portion of the treated portion of the muntin bar material, said elongated strip of covering material including an adhesive for adhering the covering material to the muntin bar material; c) bringing the muntin bar material and the covering material into contact with each other to cause the covering material to overlie and adhere to the muntin bar material and form an elongated strip of stock material which is subsequently bent to form a muntin bar; d) defining a first notch that extends inward from a first edge of said stock material; e) defining a second notch that extends inward from a second edge of said stock material; f) roll forming said elongated strip of stock material to form an enclosed structure; g) severing said enclosed structure to form a first muntin bar that includes said first notch and a second muntin bar that includes said second notch; and, h) interfitting said first notch and said second notch to form a muntin bar grid. 